An aminopeptidase activity in bovine pituitary secretory vesicles that cleaves the N-terminal arginine from beta-lipotropin60-65 |
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Authors: | H Gainer J T Russell Y P Loh |
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Institution: | Laboratory of Neurochemistry and Neuroimmunology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20205, USA |
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Abstract: | Secretory vesicles isolated from the neural and intermediate lobes of the bovine pituitary contained a membrane-bound aminopeptidase activity which cleaved arginine from beta-LPH60-65 (Arg-Tyr-Gly-Gly-Phe-Met) and Arg-MCA. Neither methionine enkephalin (Tyr-Gly-Gly-Phe-Met) nor Substance P, which has an N-terminal arginine followed by a proline, could serve as substrates for this aminopeptidase activity; nor could cathepsin B-like or chymotrypsin-like enzyme activities be detected in the vesicle preparations. Maximal enzyme activity was at pH 6.0, and the activity was inhibited by EDTA, stimulated by Co2+ and Zn2+, but was unaffected by leupeptin, pepstatin A, phenylmethylsulfonyl fluoride and p-chloromercuribenzenesulfonate, suggesting that the enzyme is a metalloaminopeptidase. The presence of this aminopeptidase activity in secretory vesicles suggests that it may be involved in peptide prohormone processing. |
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Keywords: | AminopeptidaseProhormone processing (converting) enzyme Secretory vesicle Neurohypophysis Intermediate lobe |
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